1. Field of the Invention
The present invention concerns the construction of a snowmobile. More specifically, the present invention concerns, first, a method for the design, construction, and assembly of platform for a snowmobile and, second, the platform made according to that method.
2. Description of the Related Art
The basic platform for a conventional snowmobile includes three components, a tunnel at the rear of the snowmobile, an engine cradle connected at the front of the tunnel, and a front suspension connected to the engine cradle. The three components are integrally connected to form a unitary structure that is rigid enough to withstand the forces impingent thereupon during operation of the snowmobile.
In the conventional snowmobile, the tunnel is disposed above an endless track that propels the vehicle. The engine cradle is the structural portion of the platform that extends forwardly from the tunnel and supports the engine near the front of the vehicle. The front suspension is the structural component integrated as a part of the engine cradle, located to the sides of the engine cradle. The steering skis are suspended from the front suspension, which includes shock absorbers that dampen the forces encountered by the skis as the vehicle travels over either groomed or rough terrain.
FIG. 1 illustrates the construction of one conventional snowmobile platform 10. The tunnel 12 and the engine cradle 14 are depicted in this illustration. The tunnel 12 forms the rear portion of the platform 10 while the engine cradle 14 forms the forward portion of the platform 10.
The tunnel 12 is essentially an inverted, U-shaped element. The tunnel 12 has a top portion 16, a left side portion 18, and a right side portion 20. A left side foot board 22 extends outwardly from the left side portion 18 of the tunnel 12. A right side foot board (not shown) similarly extends outwardly from the right side portion 20 of the tunnel 12.
The rear end 24 of the engine cradle 14 is attached at the front end 26 of the tunnel 12. The engine cradle 14 includes a bottom pan 28, a left side wall 30, a right side wall 32, a front portion 34, and a rear portion 36. Together, the bottom pan 28, the left side wall 30, the right side wall 32, the front portion 34, and the rear portion 36 create a rigid structure onto which the engine for the snowmobile is secured. A structural upright 38 is connected adjacent to the rear portion 36 of the engine cradle 14. The upright 38 provides structural support for the handlebar used to steer the snowmobile.
The tunnel 12 includes openings 40 through the left side 18 and through the right side 20. A drive shaft (not shown) passes through the openings 40. The drive shaft operatively connects to the endless track positioned beneath the tunnel 12 to propel the vehicle. The drive shaft also operatively connects to the engine (not shown), which sits above the bottom pan 28 of the engine cradle 14. As would be understood by those skilled in the art, motive power is transferred from the engine to the endless track via the drive shaft. The opening 40 in the left side 30 of the engine cradle 14 is also illustrated in FIG. 1. A similar opening (not shown) also passes through the right side 32 of the engine cradle 14. The openings 40 in the engine cradle 14 and the openings 40 in the tunnel 12 lie in register with one another so that the drive shaft passes through all four of the openings when the tunnel 12 and the engine cradle 14 are assembled together.
FIG. 2 illustrates one possible embodiment of the front suspension 42 for a conventional snowmobile. While the details of the engine cradle 14 in FIG. 2 differ slightly from those illustrated in FIG. 1, those skilled in the art would appreciate readily that the front suspension 42 illustrated in FIG. 2 may be incorporated as a part of the platform 10 illustrated in FIG. 1.
The left-hand side of the front suspension 42 is shown in FIG. 2. As would be appreciated by those skilled in the art, the right-hand side of the front suspension 42 is a mirror image of the left-hand side. The left-hand side of the front suspension 42 includes a ski leg 44 that is rotatably coupled to a lever arm 46. The lever arm 46, in turn, is pivotally connected to the engine cradle 14 via a structural pivot 48. The lever arm 46 pivots up and down as the snowmobile travels over the ground.
The forward end 50 of the lever arm 46 includes a bracket 52 that connects to the lower end 54 of a shock absorber 56. The upper end 58 of the shock absorber 56 connects to a bracket 60 that is, in turn, connected to the engine cradle 14 at a location 62 near a forward end thereof. The shock absorber 56 dampens the forces encountered by the ski 64 connected at the lower end of the ski leg 44.
As FIGS. 1 and 2 illustrate, the tunnel 12, the engine cradle 14, and the front suspension 42 are integrally assembled to create a rigid frame onto which the remaining elements of the snowmobile are attached.
In the construction of the conventional snowmobile platform 10, the width of the tunnel 12 and the width of the engine cradle 14 are selected as a function of the width of the endless track that propels the vehicle. While engine size typically varies from one model of snowmobile to another, the width of the endless track, and therefore the width of the tunnel 12 and the engine cradle 14, typically remains the same regardless of the size of the engine employed to propel the vehicle. This is because the width of the endless track typically remains the same for all types of snowmobiles.
There are several engine sizes typically incorporated into conventional snowmobiles, including 600 cc (cubic centimeters of displacement), 700 cc, and 800 cc varieties, for example. To accommodate each of these engine sizes, the front suspension 42 and the tunnel 12 of each platform differs from one vehicle to another. The front suspensions 42 differ between vehicle types to accommodate the variations in weight of the different engines. As a general rule, the larger the displacement volume, the heavier the engine. Therefore, the front suspension needs to be more robust. The tunnels 12 vary from one vehicle to another to accommodate different lengths of the endless track.
While the width of the endless track typically remains the same, the length of the endless track can vary from one snowmobile type to another. For a racing snowmobile, which is designed primarily for groomed surfaces, the endless track typically is shorter than the endless track incorporated into a mountain snowmobile, which is designed to operate in ungroomed (or powder) snow. Accordingly, the tunnel 12 for a racing snowmobile is generally shorter than the tunnel 12 for a mountain snowmobile. In addition, the weight of a racing snowmobile is of critical concern because unnecessary weight slows the vehicle, which is antithetical to racing.
Once the platform 10 for the vehicle is designed, the chassis for the snowmobile is designed around it. As with the platform 10, the chassis is designed to accommodate variation in the components of the vehicle.
To manufacture each new vehicle type, whether it is a racing snowmobile, a mountain snowmobile, or a hybrid variety, considerable engineering and manufacturing resources are required. Each new vehicle must be designed from the ground up. From an engineering standpoint, therefore, each new vehicle consumes a significant number of engineering hours because the platform 10 of the vehicle has to be designed from scratch. In addition, from a manufacturing standpoint, each new vehicle consumes a significant number of training hours, because the technicians responsible for assembling the vehicle must be trained to understand the construction of each new vehicle so that the vehicle may be assembled properly on the assembly line. The design and manufacture of a conventional snowmobile, therefore, is inherently inefficient both from a design and from a manufacturing standpoint, because there is a considerable duplication of effort for each new vehicle that is designed and manufactured.
Accordingly, the inefficient method of designing and manufacturing conventional snowmobiles cries out for a solution.
The prior art does not provide a solution for this inefficiency.